# Basic syntax:
find /directory/to/search -type f -exec md5sum {} + | awk '{print $1}' | sort | md5sum > single_md5sum.txt
# Where:
# - find -type f returns all files (but not directories) in
# /directory/to/search and its subdirectories
# - -exec md5sum {} obtains the md5 checksums for all files returned
# with find
# - awk '{print $1}' | sort returns the sorted md5 checksums
# - and finally, md5sum is run on the sorted list of md5 checksums to
# return one md5 checksum for all the files